For a long period of time, there has been interest in fabricating devices exhibiting negative differential resistance. In such devices, the current initially increases with increasing voltage but a point is reached after which the current decreases as the voltage increases.
Several physical mechanisms, including resonant tunneling, can be exploited in fabricating devices exhibiting such a characteristic. Perhaps the first device based on resonant tunneling was the double-barrier heterostructure proposed by Chang, Esaki and Tsu; see, for example, Applied Physics Letters, 24, pp. 593-595, June 15, 1974. The original Tsu device was a two-terminal device as were most of the other early negative differential resistance devices. More recently, a three-terminal bipolar device has been described which also exhibits negative differential resistance; see, for example, Journal of Applied Physics, 58, pp. 1366-1368, Aug. 1, 1985. This device utilizes resonant tunneling of minority carriers through a quantum well in the base region.
Though obviously the details of all these devices differ, they do have one element in common: they all utilize bulk carrier tunneling into a two-dimensional density of states, typically of electrons, in a quantum well.